1. Field of the Invention
The present invention relates to an Orthogonal Frequency Division Multiple Access (OFDMA) cellular system. More particularly, the present invention relates to a method and an apparatus for managing resources used for wireless communication.
2. Description of the Related Art
A wireless cellular communication system covers its entire service area with a plurality of Base Stations (BSs) on a division basis, and connects an air interface between each BS and each of a plurality of Mobile Stations (MSs) or Subscriber Stations (SSs) in an area of the BS, thereby providing wireless communication services to users. The air interface is connected based on wireless resources, which may be configured in a time domain, a frequency domain, or a two-dimensional time-frequency domain. More particularly, an Orthogonal Frequency Division Multiple Access (OFDMA) cellular system employs a scheme of configuring all wireless resources in a two-dimensional domain consisting of a frequency domain and a time domain, and allocating the wireless resources on a division basis according to the channel type and the user.
An Institute of Electrical and Electronics Engineers (IEEE) 802.16m system, one of the conventional OFDMA cellular systems, has a basic frame structure in which each superframe is divided into a plurality of frames and each frame is divided into a plurality of subframes. Each subframe includes a plurality of OFDMA symbols, and multiple subframes in a frame may be allocated for both or one of a Downlink (DL) transmission and an Uplink (UL) transmission, according to whether they are used in a Frequency Division Duplex (FDD) mode or a Time Division Duplex (TDD) mode.
FIG. 1 is a diagram schematically illustrating a structure of a UL subframe used in an OFDMA cellular communication system according to the related art.
Referring to FIG. 1, a UL subframe 100 is identified by symbol numbers 102 in the time domain and by distributed Logical Resource Unit (LRU) indexes 104 over the frequency domain. In the UL subframe 100 are first allocated feedback channels 112, such as a Primary Fast Feedback Channel (PFBCH) and a Secondary Fast Feedback Channel (SFBCH), and next allocated a BandWidth Request (BW REQ) channel 114, in the direction of the frequency domain, and the remaining region 116 is allocated for data bursts. In the data region 116 may be allocated a Ranging Channel (RNG CH) that an MS can use for network entry.
The IEEE 802.16m system supports an Advanced Air Interface (AAI) compared with an IEEE 802.16e system. In comparison, the IEEE 802.16e system is called a legacy system or a Wireless Metropolitan Area Networks (Wireless MAN) OFDMA system.
The IEEE 802.16m system should be able to ensure support of legacy systems with the IEEE 802.16e system. To this end, Time Division Multiplexing (TDM) is considered in a DL, and TDM or Frequency Division Multiplexing (FDM) is considered in a UL. However, in the UL, since use of TDM considerably reduces coverage, it is preferable to use FDM in order to ensure link budget of the UL.
When FDM is used in the UL, there is a need to balance loads of frequency resources for an advanced system and frequency resources for a legacy system according to the number and traffic usage of Advanced MSs (AMSs) existing in the system and capable of supporting IEEE 802.16m, and legacy MSs supporting only IEEE 802.16e. However, if the load balancing is flexibly performed, a signaling load may occur to notify the location of resources in use to an MS(s) having accessed the system. To minimize the signaling load, it is preferable for a signaling period not to be set short. In this case, since the MS should first get information about the location of resources used in the system, the latency of an MS's initial entry or handover process may increase in proportion to the signaling period.
Therefore, a need exists for a resource management method and apparatus for causing an advanced system and a legacy system to coexist based on FDM in an OFDMA cellular system.